Position sensors, for example angular position sensors for measuring an angular position of a sensor chip (e.g. mounted to a stator) relative to one or more magnets (e.g. mounted to a rotor), are known in the art.
Various magnet arrangements are used in the art, for example a two-pole bar magnet or a two-pole disk magnet or a two-pole ring magnet, or a multi-pole disk magnet, or a multi-pole ring magnet, or a plurality of individual magnets arranged on a circle, etc.
Various algorithms or formulas are used in the art, for example based on goniometric functions, Fourier functions, etc.
By measuring the strength of the magnetic field generated by the magnet(s) at various locations, it is possible to calculate the position or orientation of the magnet(s) relative to the sensor elements.
WO9854547(A1) describes a sensor arrangement comprising an angular position sensor having at least three sensitive elements and a bar magnet. A method is described how the angular position can be calculated based on an arc-tan function of a ratio of differences between sensor values. The resulting angle is relatively insensitive (robust) against a constant external magnetic field (also referred to herein as “strayfield” or “Fremdfeld”).
An advantage of using a ratio of two values, rather than the measured values themselves is that such methods are more robust against ageing effects. This principle is well known, and is used for example also in readout circuits of Wheatstone-bridges.
WO2014029885(A1) describes a sensor arrangement comprising an angular position sensor having a plurality of sensor elements arranged on a virtual circle, and comprising a multi-pole disk or multi-pole ring magnet. Depending on several parameters (e.g. the number of magnet poles, the number of sensor elements, the particular algorithm used, the orientation of the sensor elements) the resulting angle is relatively insensitive (robust) against a position error (of the sensor chip relative to the magnet), a constant external magnetic field, and in some cases, is even robust against a field gradient. The latter is especially advantageous in an automotive environment.
Various other sensor arrangements comprising one or more magnets and one or more position sensors, are known in the art, and various algorithms or mathematical functions are used, depending on the application, (e.g. a Fourier series). The various solutions address different requirements, and each solution has its own advantages and disadvantages.